Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $214.73   13.392%   $243.4866   $243.49   $243.50   $243.50  
  Purchase #2 $234.87   11.326%   $261.4714   $261.47   $261.45   $261.50  
  Purchase #3 $172.37   10.825%   $191.0291   $191.03   $191.05   $191.00  
  Purchase #4 $76.80   4.830%   $80.5094   $80.51   $80.50   $80.50  
  Purchase #5 $205.53   4.151%   $214.0616   $214.06   $214.05   $214.10  
  Purchase #6 $163.74   10.661%   $181.1963   $181.20   $181.20   $181.20  
  Purchase #7 $169.79   8.145%   $183.6194   $183.62   $183.60   $183.60  
  7 purchase totals = $1,237.83       $1,355.3738   $1,355.38   $1,355.35   $1,355.40